The next wave of consumer electronics products is incorporating not only software and hardware innovations, but also changes that have design and functional appeal. New products are being announced and released on a regular basis with some form of three dimensional (3D) glass part incorporated in them. Some examples include curved LCD TV screens, curved smart-phones and wearable gadgets (wrist phones, watches, etc.) that are either flexible or have a curved shape. Other elements of design in these types of devices are the back covers that have gone from the traditional flat glass cover plates to three dimensional curved surfaces of different styles. These innovations bring new challenges to the manufacturing processes of these 3D parts that are made of glass, which invariably need to be scratch- and impact-resistant.
The difficulty to form the different shapes has increased significantly as most of production lines were designed to handle flat two-dimensional parts. In general, these 3D parts are hot stamped and formed into the desired shape and one of the big challenges is to release the part from the hot molded oversized part to the final and finished product. Depending on the technology deployed in the existing production lines, the first step to adapt them to processing 3D shapes is to retrofit them with the necessary capability. CNC machining, for example, may need 5-axis tool movement to enable processing more complex shapes. Likewise, other technologies, such as laser, abrasive water jet, scribing and breaking, etc., will all need to be adapted to cut, mill, drill and finish some of the features on the three dimensional piece.
Other changes that add to the complexity of transitioning from 2D to 3D processing come from the material perspective. In 3D parts, the curves, bends and turns become sources of mechanical stress accumulation, which can greatly impact processing the part after it is hot formed. For example, if the part is hot stamped from an oversized glass plate, cutting and release from the matrix will be necessary, and depending on its shape, the residual stress accumulated on the curved parts can easily induce shattering of the part upon tool contact.
There are as many different methods to cut and separate glass as there are edge shapes. Glass can be cut mechanically (CNC machining, abrasive water jet, scribing and breaking, etc.), using electro-magnetic radiation (lasers, electrical discharges, gyrotron, etc) and many other methods. The more traditional and common methods (scribe and break or CNC machining) create edges that are populated with different types and sizes of defects. It is also common to find that the edges are not perfectly perpendicular to the surfaces. In order to eliminate the defects and give the edges a more even surface with improved strength, they are usually ground. The grinding process involves abrasive removal of edge material that can give it the desired finishing and also shape its form (bull nosed, chamfered, pencil shape, etc.) In order to enable the grinding and polishing steps, it is necessary to cut parts that are larger than the final desired dimensions.
The area of laser processing of materials encompasses a wide variety of applications that involve cutting, drilling, milling, welding, melting, etc. and different types of materials. Among these applications, one that is of particular interest is cutting or separating different types of substrates. However, not all of the existing laser techniques and tools lend themselves to precision cutting and finishing. Many are too abrasive, such as ablative processes, and leave a lot of defects and micro-cracks. As discussed above, defects and micro-cracks lead to weaker edges and parts and require oversized substrates to account for grinding and polishing steps until the part is finished to the desired dimensions. As a consequence, there is a great interest to have a faster, cleaner, cheaper, more repeatable and more reliable method of 3D glass shape cutting and extraction than what is currently practiced in the market today.